Korean particles 조사

Korean particles are small endings attached to a noun to show its role in the sentence.

Many come in pairs. Which one you use depends on how the word before it ends:

After a consonant (a word with batchim): 은 · 이 · 을 · 으로 · 과 · 이랑
After a vowel (no batchim): 는 · 가 · 를 · 로 · 와 · 랑

Watch 와/과: here the consonant form comes second (책과, 우유와). And 로, not 으로, also follows ㄹ (서울로). Some particles are mainly written and some mainly spoken.